British Foreign Minister Boris Johnson says Russia "may have" committed war crimes by deliberately targeting a civilian convoy on September 19 with air strikes in rebel-held parts of Aleppo. Russia denies involvement, claiming rebels fighting against Moscow's ally, Syrian President Bashar al-Assad, or a U.S. drone strike were responsible.

Meanwhile, UN envoy Staffan de Mistura says Assad's forces likely committed war crimes by repeatedly targeting civilians in Aleppo after a fragile cease-fire broke down on September 19. French Foreign Minister Jean-Marc Ayrault says even if Assad's allies, Russia and Iran, have not intentionally targeted civilians, they "will be accomplices in war crimes committed in Aleppo" if they don't pressure Syria's government to stop the strategy.

Amnesty International says it has documented many cases of Syrian government war crimes -- including torture and what the rights group calls "deliberate attacks" on hospitals, civilian residential areas, and other civilian targets. But Avner Gidron, a senior legal expert at Amnesty International, says it is difficult to state definitely that any specific attack constituting a war crime was carried out by Russian forces.

Gidron also told RFE/RL that the complications of court jurisdiction and the Syrian war's status as a noninternational armed conflict make it unlikely there will be any trials in the foreseeable future for war crimes committed there by Russia or the Syrian government.

RFE/RL: Have war crimes been committed in Syria?

Avner Gidron: War crimes have been committed in Syria by all of the [Syrian] parties. The vast majority have been committed by Syrian government armed forces and associated militia and that’s continuing on a huge scale.

There's no doubt that the vast majority has been committed by the Syrian government. You can start with the things they do to captured people. And it’s not just captured opposition fighters. It's human rights defenders, journalists, people suspected of having political sympathies for the opposition -- whether on the basis of their ethnicity or their religion, their perceived political affiliation. We’ve documented that thousands of these people have been tortured, subjected to enforced disappearance, and killed in custody. Just the torture that they've committed has been on an industrial scale.

A gutted aid truck is seen on the side of the road in the town of Orum al-Kubra on the western outskirts of Aleppo on September 20. At least 20 civilians were killed in the atttack. The United States explicitly blamed Russia for the air strike.

RFE/RL: What about the air strikes that reportedly have killed more than 230 civilians in rebel-held parts of Aleppo since the cease-fire broke down on September 19? What evidence would be necessary in a noninternational armed conflict like the war in Syria in order to define these attacks as war crimes under international law?

Gidron: It's definitely much more clearly established as a war crime in noninternational armed conflicts when a party has deliberately and directly attacked civilians or civilian objects. It's also established when attacks are inherently disproportionate. It's disproportionate when the anticipated harm to civilians would outweigh the anticipated military advantage from neutralizing a military target.

RFE/RL: Has Amnesty International collected sufficient evidence to prove Russia has carried out war crimes in Syria?

Gidron: We are not excluding the possibility that Russia is directly committing war crimes in Syria as well. It's just that we have not been able to definitely say that a particular attack, which appears to be a war crime, was committed by Russia. The problem that we have is always the same. It's been very hard for us to say "definitely by Russia" because it's the same equipment that the Syrian Air Force and the Syrian military are using. It's mostly stuff supplied by Russia.

We've researched a whole list of attacks on hospitals, medical clinics, and other civilian objects where there is reason to believe that Russia was involved. We've put all of these cases to them. Of course, they deny any role. But given the number of attacks and the way that they've been carried out, I personally would be surprised if they haven't carried out any war crimes directly in Syria. It's just that the evidence we have is relatively limited compared to the evidence we have about what the Syrian government has done or the Islamic State [militant group].

RFE/RL: Is it possible in the near future to conduct trials for war crimes in Syria?

Gidron: For these suspected war crimes by Syria itself and by Russia, there is no jurisdiction in Syria for the International Criminal Court (ICC). Syria isn't a party to it. Russia isn't a party to it. You could have the jurisdiction of the ICC with a UN Security Council referral. That's something Amnesty has been calling for now for five years. But because of the power politics and the permanent Security Council members' veto, that has not happened. Russia would never go for that.

The only way somebody could be prosecuted -- a Syrian or Russian commander who orders an attack on an aid convoy deliberately and knowing full well, not by mistake -- that could only be adjudicated through universal jurisdiction in which another state's court has jurisdiction over war crimes in a noninternational armed conflict. Another possibility, if you can’t get an ICC referral, would be to set up some sort of special tribunal. But then again, you really need the Security Council's cooperation for that.